Recent publications for several laboratories have emphasized the potential sensitivity of serum bile salt measurements in detecting liver disease. Because of technical complexity these assays have been restricted to a few laboratories.
Assay of total and individual bile salts in serum by thin layer or gas/liquid chromatography has been in limited use in clinical research for several years. Recently development of fluorimetric assays using the 3-.alpha. and 7-.alpha.-hydroxysteroid dehydrogenase enzymes from microorganisms has increased the sensitivity to levels at which serum assays are feasible. The recent availability of a purified enzyme (Sterognost 3-.alpha.) may increase the specificity of this assay. Nonetheless extraction is still required before assay.
Recently, radioimmunoassay of various bile salts has simplified the assay procedure and allowed measurement of individual bile salts in serum from normal individuals. These radioimmunoassays are based on tritiated bile salts or .sup.35 S (in the case of sulfated bile salts), these being .beta.-emitting tracers. Wide clinical usage has not yet been achieved perhaps because (a) clinical bile salt measurements are of uncertain value; (b) equipment required (liquid scintillation counter) for tritium based RIA are cumbersome, expensive and not widely available; (c) the expense of a tritium based assay (equipment, scintillation fluor and counting vials) cannot be justified in many clinical labs; and (d) low specific activity tracers and low antibody titers make antibody supply uncertain. Uncertainty of the clinical value of serum bile salt measurement is being clarified and clinical studies utilizing these assays will increase in frequency. Already it has been shown that serum bile salt measurements were the earliest predictor of relapse in chronic active hepatitis. The remaining problems would be largely obviated by a high specific activity tracer such as .sup.125 I, a .gamma.-emitting radionuclide. The common bile salts, however, do not have a site which can be iodinated.
Various compounds which have no site for iodination--adrenal steroids, testosterone, estrogens and cyclic nucleotides--have been chemically modified by addition of histamine, tyrosine, tyrosine methyl ester, or phenylpropionic acid which can be iodinated. These derivatives have provided .sup.125 I based immunoassays for these compounds.
The specific activity of radioiodinated bile salts would approach 2000 Ci/mMole as opposed to 3.5 Ci/nM for .sup.3 H tracers. The increased specific activity would allow increased sensitivity and increased antibody liters and could be quantitated using the .gamma.-spectrometer instead of liquid scintillation spectrometers. In addition the .gamma.-emitting derivative, if physiologically active, could be useful for physiologic studies of transport or absorption of bile salts. Blood clearance of bile salts and hepatic uptake and excretion could be measured; hepatic and biliary and intestinal scintigraphy or quantitative scintigraphy could be performed and ileal absorptive function could be quantitated. The common bile salts, however, have no group which can be iodinated easily.
It is an object of this invention to provide bile salt derivatives which can be iodinated easily.
A further object of this invention is to provide radioiodinated bile salt derivatives.
An additional object of this invention is to provide methods for purifying such derivatives.
Other objects of the invention are to use such radioiodinated bile salt derivatives in radioimmunoassays, the measurement of hepatic uptake and excretion, and scintigraphy.
Other objects of this invention will be apparent hereinafter.